This invention relates generally to the removal of a partial or total occlusion from a blood vessel by generating pressure waves within the vessel through optical fiber media, and, more specifically, to the removal of a blood clot from a vessel within the human brain. The term xe2x80x9cclotxe2x80x9d is used herein to refer to a thrombus, embolus or some other total occlusion of a vessel.
Medical procedures to open a partially or totally blocked blood vessel are available. Angioplasty has long been used to restore full blood flow in a coronary artery by mechanically deforming deposits on the arterial walls but has been less successful to open a totally occluded vessel. Laser techniques have been proposed to directly ablate obstructing material from arteries, such as plaque and certain types of clots, by inserting optical fibers into the artery to the point of the obstructing material but these techniques have enjoyed only limited success in practice. Various uses of ultrasonic energy to generate acoustic waves directed against plaque or a clot within an artery to mechanically break up the obstructing material have also been proposed but medical procedures utilizing these techniques have not enjoyed widespread acceptance. Photo acoustic techniques have been proposed for vasodilation and the break-up of plaque and clots in arteries, wherein one or more optical fibers are inserted into the vessel and pulses of radiation delivered to the vessel through the fibers generate a pressure or acoustic wave directed against the obstruction.
Major blood vessels within the brain are very small, generally not exceeding three millimeters in diameter and being much smaller than that in most places. Most cerebral blood vessels decrease in diameter along their lengths until becoming capillaries. Besides being small, the walls of cerebral vessels are more fragile than those of vessels in other parts of the body and are more loosely connected to surrounding tissue.
When a thrombus is formed or an embolus is lodged in a blood vessel of the brain, an ischemic stroke results. The resulting sudden cut off of the supply of fresh blood to cerebral vessels terminates the supply of oxygen to these vessels and to the brain tissue they supply. The seriousness of a stroke depends upon the amount of brain tissue involved and its location. Generally, the more serious strokes result when the larger cerebral vessels become blocked, since they supply more volume of tissue than the smaller vessels, but the blockage of vessels having a diameter of less than one millimeter, or even one-half of one millimeter or less, can be quite serious.
If a cerebral vessel of a stroke victim can be unblocked within about six hours after the blood flow is totally stopped, the effects of the stroke on the oxygen starved brain tissue are often largely reversed. If unblocked within this time, deterioration of the walls of the blocked vessel to the point of hemorrhaging is prevented. As a result, many have tried to develop techniques for removing clots from cerebral vessels within a few hours after a stroke has occurred.
One such technique is to position a catheter into the blocked vessel to mechanically remove the clot. But this is very difficult to do without causing further damage because the vessels are so small, contain very sharp turns, are weakly constrained and have fragile walls. Alternatively, a lytic drug is often applied intravenously, in an attempt to dissolve the clot without having to dislodge it mechanically. In an attempt to improve the rate of success of the lytic drug, it has been introduced directly into the blocked vessel through a catheter at the point of the blockage. But none of these techniques have enjoyed a high rate of success.
Therefore, it is a primary object of the present invention to provide techniques for reopening clotted blood vessels of the human brain with an increased rate of success.
It is another important object of the present invention to provide techniques to remove partial or total occlusions from other parts of the body.
It is a further object of the present invention to provide techniques for removing obstructions from the human body, particularly clots from cerebral blood vessels, without causing collateral damage to the vessel.
It is another object of the present invention to provide a practical instrument and system to perform these functions.
These and other objects are accomplished by the various aspects of the present invention, wherein, briefly and generally, a catheter containing multiple small diameter optical fibers terminating in a two-dimensional pattern is positioned adjacent the occlusion and pulses of radiation are directed along the optical fibers, one at a time in sequence, with the individual pulses having a duration and amount of energy sufficient to generate a shock wave and, from an expansion and collapse of a bubble, a pressure wave, both of which are directed against the obstruction in order to break it up and restore the flow of blood through the vessel. Clots within either arteries or veins are emulsified in this manner.
It has been found that the use of very small diameter optical fibers allows the desired shock and pressure waves to be generated with a relatively low amount of radiation pulse energy, thereby keeping the amount of heat input to the vessel at a low level. Proper thermal management according to the present invention reduces the likelihood of damaging the walls of the blood vessel adjacent the occlusion, which is especially important for the relatively thin walled vessels of the brain. Further, it is desirable that radiation pulses not being efficiently converted into the desired pressure waves be terminated in order to prevent inputting energy that heats the region without doing useful work. In addition to keeping the power input low, a liquid coolant may be introduced through the catheter to carry heat away from the region of the occlusion during the treatment.
Additional objects, features and advantages of the various aspects of the present invention will be better understood from the following description of its preferred embodiments, which description should be taken in conjunction with the accompanying drawings.